A variety of data mining systems and methods are known for detecting associations between items stored or represented in a database and users who may be interested in the items. For example, in the context of an electronic catalog system that provides a large variety of items, a system may monitor user interactions (e.g., viewing, purchasing, downloading, commenting, rating, reviewing, etc.) with the items. Based at least partly on the monitored interactions, the system's data mining processes may determine a user's favorability, affinity, or other associations with individual items that the user has interacted with. The user's affinities for particular items in combination with applicable item-to-item associations can be used to select additional items to recommend to the user. A same computer or user account, however, may be shared by multiple people (e.g., family members), which may result in recommendations that are not tailored to the interests of any particular person.